Development and improvement in the design and construction of waterbeds has progressed to a point where such devices are more accurately to be referred to as flotation sleep systems. Such a term refers to a liquid-filled bed consisting of a conventional ticking cover, a soft-sided frame intended to contain a water mattress, a water mattress, and a water mattress liner provided to capture and contain the liquid in the supporting structure should rupture occur to the water mattress. In addition, most such systems incorporate a heating element by which a comfortable temperature can be maintained within the supporting liquid. Recent developments have produced designs which have the advantages of waterbeds without the disadvantages of high heating costs, a non-conventional look, or the need for special linens and blankets. Some flotation sleep systems have controlled head-to-foot and side-to-side liquid movement, are lighter in weight using less water, adapt to existing bedroom furniture and use conventional bedding.
A type of design gaining increasing popularity is generally described in U.S. Pat. No. 4,221,013. This particular type of construction locates a water filled bladder or plurality of water filled bladders within an inner foam framework. The inner foam framework supports or cradles the water filled elements from below by extending across the entire bottom and up along the periphery of the mattress. An outer foam frame and cover encloses the entire structure from above and is configured to slip down over the outside of the inner framework's side walls. An inherent disadvantage of such a construction is that the outer cover slips off the inner framework as easily as it is slipped thereon. Consequently, any bedding that is merely tucked under the outer framework is easily dislodged. The inner framework acts as a barrier effectively preventing bedding from being tucked in any further than the width of the outer framework. Since the inner framework is disposed under and within the outer framework and top cover, the inner framework cannot be grasped and lifted so as to allow the insertion of bedding thereunder. Solutions to conveniences or disadvantages of this nature would allow waterbeds to continue gaining in popularity.